I will show how the statistical models that are used to describe the performance of atomic clocks are derived from their internal design. These statistical models form the basis for time scales, which are used to define international time scales such as International Atomic Time and Coordinated Universal Time. These international time scales are realized by ensembles of clocks at national laboratories such as the National Institute of Standards and Technology, and I will describe how ensembles of atomic clocks are characterized and managed.

The uncertainty (accuracy) in the realization and dissemination of the SI second is determined by the characteristics of three major components: (1) primary frequency standards, (2) time scale flywheels that provide a continuously present frequency reference, and (3) frequency transfer systems. Currently these three systems contribute at approximately equal levels in the mid 10−16 range over 20 to 30 days of averaging time to the practical delivery of the SI second to the most demanding users. Any significant improvement in one system requires similar improvements in the other two systems in order for most users to see the full benefits.

A capillary absorption spectrometer (CAS) suitable for IR laser isotopeanalysis of small CO2 samples is presented. The system employs a continuous-wave (cw) quantum cascade laser to study nearly adjacent rovibrational transitions of different isotopologues of CO2 near 2307 cm−1 (4.34 μm). This initial CAS system can achieve relative isotopic precision of about 10 ppm 13C, or ∼1‰ (per mil in delta notation relative to Vienna Pee Dee Belemnite) with 20–100 picomoles of entrained sample within the hollow waveguide for CO2 concentrations ∼400–750 ppm. Isotopic analyses of such gas fills in a 1-mm ID hollow waveguide of 0.8 m overall physical path length can be carried out down to ∼2 Torr. Overall 13C/12C ratios can be calibrated to ∼2‰ accuracy with diluted CO2 standards. A novel, low-cost method to reduce cw-fringing noise resulting from multipath distortions in the hollow waveguide is presented, which allows weak absorbance features to be studied at the few ppm level (peak-to-rms) after 1000 scans are co-added in ∼10 s. The CAS is meant to work directly with converted CO2 samples from a laser ablation-catalytic combustion micro-sampler to provide 13C/12C ratios of small biological isolates currently operating with spatial resolutions ∼50 μm.

A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-rayphoton energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemissionspectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances.

Penning traps are made extremely compact by embedding rare-earth permanent magnets in the electrode structure. Axially-oriented NdFeB magnets are used in unitary architectures that couple the electric and magnetic components into an integrated structure. We have constructed a two-magnet Penning trap with radial access to enable the use of laser or atomic beams, as well as the collection of light. An experimental apparatus equipped with ion optics is installed at the NIST electron beamion trap (EBIT) facility, constrained to fit within 1 meter at the end of a horizontal beamline for transporting highly charged ions. Highly charged ions of neon and argon, extracted with initial energies up to 4000 eV per unit charge, are captured and stored to study the confinement properties of a one-magnet trap and a two-magnet trap. Design considerations and some test results are discussed.

We propose and develop a method to quickly and precisely determine the polarization direction of coherent terahertz electromagnetic wavesgenerated by femtosecond laser pulses. The measurement system consists of a conventional terahertz time-domain spectroscopy system with the electro-optic (EO) sampling method, but we add a new functionality in the EO crystal which is continuously rotating with the angular frequency ω. We find a simple yet useful formulation of the EO signal as a function of the crystal orientation, which enables a lock-in-like detection of both the electric-field amplitude and the absolute polarization direction of the terahertz waves with respect to the probe laser pulse polarization direction at the same time. The single measurement finishes around two periods of the crystal rotations (∼21 ms), and we experimentally prove that the accuracy of the polarizationmeasurement does not suffer from the long-term amplitude fluctuation of the terahertz pulses. Distribution of the measuredpolarization directions by repeating the measurements is excellently fitted by a Gaussian distribution function with a standard deviation of σ = 0.56°. The developed technique is useful for the fast direct determination of the polarization state of the terahertz electromagnetic waves for polarizationimaging applications as well as the precise terahertz Faraday or Kerr rotation spectroscopy.

We report on design and performance of a high-resolution x-raymonochromator with a spectral bandwidth of ΔEX ≃ 1.5 meV, which operates at x-ray energies in the vicinity of the backscattering (Bragg) energy EH = 13.903 keV of the (008) reflection in diamond. The monochromator is utilized for high-energy-resolution diffraction characterization of diamond crystals as elements of advanced x-ray crystal optics for synchrotrons and x-ray free-electron lasers. The monochromator and the related controls are made portable such that they can be installed and operated at any appropriate synchrotron beamline equipped with a pre-monochromator.

We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere. The system performance is tested by measuring the anion momentum distributions from two DEA resonances, namely H− from H2O− (2B1) and O− from (2Πu). The results are compared with existing experimental and theoretical data.

We demonstrate single mode operation of an external cavitydiode laser (ECDL) employing an interference filter with multimode bandwidth for mode selection. A cateye reflector maximizes feedback efficiency and reduces susceptibility to intra-cavity optical misalignment. Narrow linewidths of 26 kHz are observed, and the laser can be tuned over 14 nm using a single 785 nm filter, without alteration of the output beam direction. The cateye reflector and filter allow a mechanically rigid design free of significant mechanical resonances, illustrated by comparison of the frequency noise spectrum with that of a common Littrow ECDL design using a diffraction grating and kinematic mount.

A photonic force microscope comprises of an optically trapped micro-probe and a position detection system to track the motion of the probe. Signal collection for motion detection is often carried out using the backscattered light off the probe–however, this mode has problems of low S/N due to the small backscattering cross sections of the micro-probes typically used. The position sensors often used in these cases are quadrant photodetectors. To ensure maximum sensitivity of such detectors, it would help if the detector size matched with the detection beam radius after the condenser lens (which for backscattereddetection would be the trapping objective itself). To suit this condition, we have used a miniature displacement sensor whose dimensions makes it ideal to work with 1:1 images of micrometer-sized trapped probes in the backscatteringdetection mode. The detector is based on the quadrant photo-integrated chip in the optical pick-up head of a compact disc player. Using this detector, we measured absolute displacements of an optically trapped 1.1 m probe with a resolution of ∼10 nm for a bandwidth of 10 Hz at 95% significance without any sample or laser stabilization. We characterized our optical trap for different sized probes by measuring the power spectrum for each probe to 1% accuracy, and found that for 1.1 μm diameter probes, the noise in our position measurement matched the thermal resolution limit for averaging times up to 10 ms. We also achieved a linear response range of around 385 nm with cross talk between axes ≃4% for 1.1 μm diameter probes. The detector has extremely high bandwidth (few MHz) and low optical power threshold–other factors that can lead to its widespread use in photonic force microscopy.

We have developed a soft x-raytime-resolvedphotoemissionspectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemissionspectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

We developed a compact terahertz (THz) spectrometer with a superconductor-insulator-superconductor (SIS) mixer, aiming to realize a portable and highly sensitive spectrometer to detect dangerous gases at disaster sites. The receiver cryostat which incorporates the SIS mixer and a small cryocooler except for a helium compressor has a weight of 27 kg and dimensions of 200 mm × 270 mm × 690 mm. In spite of the small cooling capacity of the cryocooler, the SIS mixer is successfully cooled lower than 4 K, and the temperature variation is suppressed for the sensitive measurement. By adopting a frequency sweeping system using photonic local oscillator, we demonstrated a spectroscopic measurement of CH3CN gas in 0.2–0.5 THz range.

Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beamcurrent density was around 0.37 mA/cm2 with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beamcurrent density extracted from the source was 0.57 mA/cm2 for a 50 eV ion beam and 1.78 mA/cm2 for a 100 eV ion beam.

The discharge gas pressure is a key factor to influence the extracted current of ion source. In this paper, the dependence of extracted current on discharge gas pressure was investigated in detail at different arc discharge currents. The discharge gas pressure with a very broad range (0.1 Pa–2.7 Pa) was scanned for the first time. It is turned out that, with the increasing of discharge gas pressure, the extracted current increases and the arc voltage decreases at different arc currents; however, when the discharge gas pressure exceeds a certain value, the extracted current decreases. For the same discharge gas pressure, the higher the arc current, the higher the arc voltage and the extracted current are. The arc efficiency was also calculated, and its dependence on gas pressure was almost the same with the dependence of extracted current on gas pressure, but at the same discharge gas pressure, the lower the arc current, the higher the arc efficiency is and the lower the extracted current is.

A new numerical Monte Carlo method based model of a hot cavitysurface ionizationion source is presented in this paper. The model, intended to support the studies on ionization phenomena in a widely used class of ion sources, takes into account geometry of the ion source and extraction system, ionizer temperature and other features. The results of ion source efficiency calculations for various configurations of the extraction field are reviewed. The dominant role of the ionizer region near the extraction opening is described. Simulated dependences of ionization efficiency on the working parameters like ionizer length and temperature, ionization potential of the substance, and extraction voltage are discussed. A good agreement of the experimental data (e.g., influence of ionizer temperature, current-voltage curve) and the predictions of the model is found. It is also shown that the contribution to the ionization yield from impact of thermionic electrons accelerated by the extraction field may be significant, especially for the substances of small surface ionization coefficient. The simulation results are compared to the predictions of different theoretical models of the ion source—the obtained simulation data are in accordance both with a well-known Kirchner formula and the so called spherical ionizer model.

The lithiumbeamdiagnostic at ASDEX Upgrade routinely delivers electron density profiles in the plasma edge by lithiumbeam impact excitation spectroscopy. An accurate background subtraction requires a periodically chopped lithiumbeam. A new, improved chopping system was developed and installed. It involves a voltage modulation for the extractor electrode and the beam deflection plates. The modulation of the extractor electrode reduces the unused portion of lithium ions and improves the stability of the beam with respect to its position. Furthermore, the data indicate an extended emitter lifetime. The extractor chopping was also found to be insensitive to sparks. The deflection chopping experiments demonstrated beam chopping in the kilohertz range. The significantly higher modulation frequency of the deflection chopping improves background subtraction of fast transient events. It allows a more accurate density measurements in the scrape off layer during impurity injections and edge localized modes.

We have measured ion temperature as well as electron temperature in plasma blobs observed in a linear plasma device by using an improved ion sensitive probe. Current–voltage characteristics of the ion sensitive probe inside and outside plasma blobs were re-constructed with a conditional sampling method. It is clearly found that both ion and electron temperatures in plasma blobs decrease more slowly in a cross-field direction than those in a bulk plasma without plasma blobs.

The method of tracer-encapsulated solid pellet (TESPEL) is now flourishing in various fields. The original purpose to study impurity transport without giving substantial perturbation on the plasma is implemented successfully for years. In addition to this, TESPEL is being intensively applied to study thermal (especially non-local) transport, high energy particles with the use of TESPEL ablation cloud, and spectroscopy from the viewpoint of atomic data. It is now further growing up to the utilization of multiple tracer methods which was not planned at the initial phase of the project. The proof-of-principle experiment using triple tracers has been successfully implemented. This opens a way to compare the Z dependence or mass dependence of impurity transport. In this article, as TESPEL is used in a variety of fields, the TESPEL injection system is summarized together with the method of TESPEL production, TESPEL storage disk, TESPEL guide system, and the differential pumping system. Also, the observation system for TESPEL flight and TESPEL ablation is explained.

The interaction between two ns-laser-induced plasmas in air at the early-stage of expansion has been analyzed by using a method based on the direct measurement of the perturbation of an externally applied electric field. In this experimental method, the plasmas were produced by focusing two laser beams between the plates of a parallel-plane-charged capacitor. These plasmas produce a perturbation in the electric field of the capacitor which can be measured as a voltage change across a resistor connected to the ground plate. It was found that for delays shorter than 5 ns, the interaction between plasmas is mainly due to the interaction of the dipole-charge distribution of each plasma. For longer time delays, the shielding effect was dominant.